Although many brazing modes have been employed to join aluminum pieces together, they can be divided principally into the flux and fluxless methods. In a fluxless brazing method, a high vacuum is required to eliminate the formation of oxides which inhibit bonding. The use of a vacuum is disadvantageous because of the time required to pump air out of the brazing chamber and because of the necessity for a good vacuum apparatus which is expensive. The filler metal typically employed for fluxless aluminum brasing is an aluminum alloy typically containing 7.0-8.0% silicon and 1.5-2.5% magnesium.
With a flux method, a chemical is coated onto the surfaces to be joined and is displaced by the brazing filler metal under proper heat conditions. Although this method is cheaper because it is carried out under ambient atmosphere conditions, there often is left a flux residue which promotes galvanic corrosion. Accordingly, the brazed part must be subjected to a complicated cleaning procedure following brazing, but even this cleaning procedure is not capable of removing all the chemicals completely. Accordingly, a flux type brazing method will not achieve the strength of fluxless vacuum brazing. A typical filler metal employed for the flux type method is an aluminum alloy containing only 6-12% silicon.
What is needed is a brazing method which has the economy and versatility of a flux type method, coupled with the increased wetting characteristics of a fluxless type of method.